The long term goal of our research is to understand the anatomic and biochemical factors that control aqueous outflow resistance in the normal eye, and the pathophysiologic changes that occur in the glaucomatous eye. Our overall hypothesis: In the normal eye, the extracellular matrix (ECM) underlying the cells of Schlemm's canal creates the majority of aqueous outflow resistance, with the canal cells contributing about 22% of the resistance through their interaction with the ECM. This ratio is unknown in POAG. Three hypothesis arise from this, based upon findings from our completed grant, and will be tested in our current proposal: 1) Although the ECM is primarily responsible for aqueous outflow resistance, the ECM is made by trabecular cells, and outflow resistance is ultimately a """"""""cellular"""""""" process. Trabecular cells can respond to stimuli and change their synthetic profile. Two clinical findings will be studied. Both findings involve molecules that induce cellular changes in other tissues. They are prototypes to test if TM cells respond in the same way, and if TM cell changes can affect IOP: (1) TGF-beta2 is increased in the aqueous of POAG eyes. We believe it is the fundamental mechanism for the development of POAG. It causes increased IOP in cultured human eyes, and may be the long-sought model for the pathogenesis of POAG (aim 1). (2) Prostaglandin treatment decreases IOP clinically, and also in cultured eyes. The mechanism of prostaglandins in lowering IOP remains contested: although all studies agree it increases uveoscleral outflow, they disagree on its effect on the TM. We believe PG affect trabecular cells to decrease IOP (aim 2). 2) The small increase of ECM in POAG indicates an """"""""anatomic plug"""""""" is not present. Instead, POAG is a derangement of a physiologic process, best found by comparisons with normal eyes. Both biochemical and structural evidence will test this hypothesis. Myocilin is present in aqueous, and can increase IOP in cultured eyes. Aqueous levels in normal eyes and POAG are unknown. If elevated in POAG, this would be missed by microscopy: not seen as an """"""""anatomic plug"""""""" (aim 3). A change in the cellular properties of the canal cells in glaucoma (""""""""stiffer"""""""" or more adherent cells that resist aqueous outflow) could elevate IOP but would not be seen by microscopy. Removal of Schlemm's canal cells in POAG should determine their contribution to outflow resistance (aim 4). 3) Regions of the TM where Schlemm's canal cells do not sit on ECM (""""""""expanded JCT configuration"""""""") have less outflow resistance due to loss of the canal cell-ECM interaction. This expanded JCT configuration differs significantly from the classic large lumen Schlemm's canal. These regions will be """"""""preferential flow"""""""" regions, and aqueous tracers should appear in these regions first. If this occurs, it would change our basic understanding of how aqueous passes through the TM (aim 5).
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